Storage system and backup method

ABSTRACT

Differential management information that is information representing the difference between a logical volume and a sequential device group after a full backup is updated in response to an update of the logical volume. Partial data that are data representing the difference between the logical volume and sequential device group are specified by using the updated differential management information, information necessary for restoration that is necessary to restore the data group located in the updated logical volume by using the partial data is recorded in the sequential device group, and the partial data are backed up from the updated logical volume into the sequential device group.

CROSS-REFERENCE TO PRIOR APPLICATION

This application relates to and claims the benefit of priority fromJapanese Patent Application No. 2006-237671, filed on Sep. 1, 2006 theentire disclosure of which is incorporated herein by reference.

BACKGROUND

The present invention generally relates to data backup technology.

For example, Japanese Patent Application Laid-open No. H11-212875discloses a method by which in a storage subsystem including a primarysubsystem and a secondary subsystem, the primary subsystem performs fullbackup and differential backup of data received from a higher-leveldevice in the secondary subsystem. Furthermore, a method for performingdata restoration from the data backed up in the secondary subsystem isalso disclosed.

For example, there exist methods by which a computer, a disk storage,and a tape library device are connected to a communication networktermed SAN (Storage Area Network) and data stored in the disk storageare backed up to the tape library device by a server for processing ofbackup (referred to hereinbelow as “backup server”). In this case, thedata that are the backup object are backed up via the backup server. Theresultant problem is that the backup performance depends on the backupserver, and when the processing performance of the backup server is low,the time required for the backup is increased.

A similar problem is also encountered, for example, when the backed-updata are restored in the processing flow that is inverted with respectto the backup, more specifically, when data are restored from the tapelibrary device to the disk storage via the backup server.

Those problems can be resolved by the backup method disclosed inJapanese Patent Application Laid-open No. H11-212875. However, with thisbackup method, in the case of differential backup, data are recorded ona tape, and the information necessary to restore the data, for example,information for managing the difference between the data (referred tohereinbelow as “differential data information”) is stored in the controlmemory of the secondary subsystem. For this reason, the processing ofdata restore is performed by using both the data recorded on the tapeand the differential data information stored in the control memory ofthe secondary subsystem. The resultant problem is that, for example,when the information of the control memory of the secondary subsystem islost due to an accident or the like, the differentially back-up datacannot be restored.

Yet another problem is that in order to perform differential backup ofmultiple generations to store the differential data information in thecontrol memory of the secondary subsystem, the control memory has tohave a storage capacity enabling the memory to store the differentialdata information of each generation, and the number of generations forwhich the differential backup is performed is limited by the storagecapacity of the control memory.

Such problem is not limited to differential backup and is alsoencountered in the case of a backup of a type such that restorationcannot be performed if the information that is necessary for therestoration (referred to hereinbelow as “information necessary forrestoration”), such as differential data information, is absent (forconvenience, such backup will be referred to hereinbelow as “partialbackup”), for example, when an incremental backup is performed.

SUMMARY

Accordingly, an aspect of the present invention enables the backup andrestoration that do not require a backup server and can restore datathat are partially backed up, even when the information necessary forrestoration is absent in the storage subsystem performing the backup.

Another aspect of the present invention prevents the number ofgenerations that can be differentially managed from being limited to thestorage capacity of the memory of the storage subsystem.

Other aspects of the present invention will become clear from thefollowing description.

The storage system in accordance with the present invention has aplurality of storage devices of a sequential access type that arestorage devices of a type that can process a sequential access at a highspeed, but cannot process a random access at a high speed, and at leastone storage device of a random access type that is a storage device of atype that can process a random access faster than the storage devices ofa sequential access type, and backs up data located in a logical volumeon the at least one storage device of a random access type in thestorage devices of a sequential access type. This storage systemcomprises a full backup section that executes a full backup by which alldata located in the logical volume are backed up from the logical volumeto a sequential device group comprising the plurality of storage devicesof a sequential access type, a differential management informationstorage section that stores differential management information that isinformation representing a difference between the logical volume and thesequential device group after the full backup, a differential managementsection that updates the differential management information in responseto an update of the logical volume, and a partial backup section thatexecutes a partial backup by which partial data that are data equivalentto a difference between the logical volume and the sequential devicegroup are specified by using the updated differential managementinformation, information necessary for restoration that is necessary torestore a data group located in the updated logical volume by using thepartial data is recorded in the sequential device group, and the partialdata are backed up from the updated logical volume to the sequentialdevice group. A variety of storage devices such as hard disks and flashmemories can be employed as the storage devices of a random access type.Likewise, a variety of storage devices such as magnetic tapes can beemployed as the storage devices of a sequential access type.

This storage system can be configured, for example, using one or aplurality of storage subsystems. For example, a higher-level device suchas a host computer or another storage subsystem may be connected to onestorage subsystem.

Furthermore, new data relating to the logical volume may be written intothe logical volume or they may be written into a separate logical volumeassociated with the logical volume. In the latter case, the updatedlogical volume can be a combination of the logical volume and theseparate logical volume.

In the first embodiment, the partial backup section includes the updateddifferential management information in the information necessary forrestoration. The differential management section resets the updateddifferential management information in the case where the partial backupis conducted, and updates the reset differential management informationin the case where the logical volume is thereafter updated.

In the second embodiment, the differential management information is abitmap. Each bit of the bitmap corresponds to each volume portion of thelogical volume. The partial backup section includes a storage size ofthe volume portion corresponding to the bit of the bitmap and a storagecapacity of the logical volume in the information necessary forrestoration.

In the third embodiment, a backup management storage section is furtherprovided, and this backup management storage section stores backup unitmanagement information representing, as a backup unit, a storage area ofthe sequential device group, that has been consumed by a backup to thesequential device group.

In the fourth embodiment, the configuration of the third embodimentfurther comprises a backup unit management section that adds, to thebackup unit management information, information representing, as onebackup unit, the storage area that has been consumed by the backup whenthe full backup or the partial backup is completed.

In the fifth embodiment, at least one storage device of a random accesstype of the fourth embodiment has a plurality of logical volumes. Thepartial backup section performs the partial backup with respect to eachof the plurality of logical volumes. The backup unit management sectiontakes a storage area comprising each data that is recorded by eachpartial backup as the backup unit.

In the sixth embodiment, in the configuration of the fourth embodiment,the backup unit management section includes a backup unit identifier, abackup class representing a class of backup, and a sequence informationrepresenting a sequence of backup for each backup unit in the backupunit management information. The partial backup section specifies abackup unit having recorded therein backup of data necessary forrestoration of the partial backup based on sequence information andbackup class in the backup unit management information and includes abackup unit identifier of the specified backup unit and a backup classindicating that this is a partial backup in the information necessaryfor restoration.

In the seventh embodiment, the partial backup section records theinformation necessary for restoration on the upstream side of thesequential device group from the partial data.

In the eighth embodiment, the partial backup section records theinformation necessary for restoration and the partial data on thedownstream side from all the data that are recorded by the full backup.

In the ninth embodiment, a restore section is further provided thatrestores the updated logical volume by using the information necessaryfor restoration that is recorded in the sequential device group.

In the tenth embodiment, in the configuration of the ninth embodiment,the differential management information is a bitmap. Each bit of thebitmap corresponds to each volume portion of the logical volume. Thepartial backup section includes a storage size of the volume portioncorresponding to the bit of the bitmap and a storage capacity of thelogical volume in the information necessary for restoration. The restoresection restores the updated logical volume based on the storage sizeand the storage capacity contained in the information necessary forrestoration.

In the eleventh embodiment, the logical volume is a secondary logicalvolume from a volume pair comprising a primary logical volume, which isa copy source, and the secondary logical volume, which is a copydestination. The primary logical volume and secondary logical volume maybe in one storage subsystem or in different storage subsystems.

In the twelfth embodiment, the partial backup is any one of adifferential backup and an incremental backup.

In the thirteenth embodiment, the differential management information isa bitmap. Each bit of the bitmap corresponds to each volume portion ofthe logical volume. The partial backup section includes the updatedbitmap, a storage size of the volume portion corresponding to the bit ofthe bitmap, and a storage capacity of the logical volume in theinformation necessary for restoration, records the information necessaryfor restoration and the partial data on the downstream side from all thedata that are recorded by the full backup, and at this time records theinformation necessary for restoration on the upstream side of thesequential device group from the partial data. The differentialmanagement section resets the updated bitmap in the case where thepartial backup is conducted and updates the reset bitmap in the casewhere the logical volume is thereafter updated. The partial backup isany one of a differential backup and an incremental backup.

In the fourteenth embodiment, in the configuration of the thirteenthembodiment, a bitmap for a differential backup and a bitmap for anincremental backup are present as the bitmap. In the case of theincremental backup, the bitmap for incremental backup is included.

The above-described storage sections can be configured of storageresources such as memories. Furthermore, other sections can beconfigured of hardware, computer programs, or combinations thereof (forexample, some are implemented of computer programs and the rest ofhardware). A computer program is executed by reading with apredetermined processor. Furthermore, a storage area present on ahardware resource such as a memory may be used appropriately duringinformation processing performed by reading a computer program with aprocessor. A computer program may be installed from a recording mediumsuch as a CD-ROM into a computer or may be downloaded into a computervia a communication network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration example of a computer system of the firstembodiment of the present invention;

FIG. 2 illustrates a configuration example of a controller 123 of astorage subsystem 101;

FIG. 3 illustrates an example of management information held byManagement 215 Volume Pair;

FIG. 4 shows an example of logical image of a tape pool 401 managed byManagement 218 of Tape;

FIG. 5 shows an example of storage information of a tape group 411;

FIG. 6 shows an example of management information held by the Management218 of Tape;

FIG. 7 shows an example of management information held by a Management211 of Backup Data;

FIG. 8 shows an example of recording format of a tape 136;

FIG. 9 shows an example of management information recorded on a tapeduring full backup;

FIG. 10 shows an example of management information recorded on a tapeduring differential/incremental backup;

FIG. 11 shows a processing flow relating to the case where the storagesubsystem 101 receives a write request from the host computer 100 to adisk 124;

FIG. 12 shows a processing flow of Preprocessing of Backup;

FIG. 13 shows a processing flow of Processing of Full Backup;

FIG. 14 shows a processing flow of Processing of Differential Backup;

FIG. 15 shows a processing flow of Processing of Incremental Backup;

FIG. 16 shows a processing flow of Processing of Restore;

FIG. 17 shows a processing flow of Processing of Restore following theprocessing shown in FIG. 16;

FIG. 18 shows a processing flow of Processing of Restore following theprocessing shown in FIG. 17;

FIG. 19 shows a processing flow of Processing of Pair Re-Synchronizing(Usual); and

FIG. 20 shows a processing flow of Processing of Pair Split.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Several embodiments of the present invention will be described belowwith reference to the appended drawings. In the explanation below, threetypes of backup will be considered: full backup, differential backup,and incremental backup. Of the backups of those three types, thedifferential backup and incremental backup are backups of the typesbelonging to partial backup. When two or more backup types of theaforementioned three types of backup are referred to, they will bedescribed by using a slash “/”. For example, when all three types ofbackup are indicated, they will be described asfull/differential/incremental backup. The symbol “/” herein is used inthe meaning of “and/or”.

Embodiment 1

For example, in the first embodiment, the storage system is one storagesubsystem, the higher-level device is a host computer, the storagedevice of a random access type is a magnetic disk (referred tohereinbelow simply as “disk”), and the storage device of a sequentialaccess type is a magnetic tape (referred to hereinbelow simply as“tape”).

In the first embodiment, a management terminal connected to the storagesubsystem is provided. Furthermore, a tape library device comprising aplurality of tapes and a controller that controls the disk and tapelibrary device is provided in the storage subsystem.

The controller comprises a Disk Control Program that controls the disk,a Tape Library Control Program that controls the tape library device,and a Backup/Restore Control Program that performs copy control from thedisk to the tape.

The tape library device comprises a robot that transfers the tapes, atape drive that reads/writes (accesses) the tapes, and a tapeexport/import slot for exporting/importing the tapes from and to thetape library device.

The host computer comprises an application performing write/read of datafrom and to the storage subsystem, a Program of Volume Pair ControlIndication that transmits a Volume Pair Control Indication to thestorage subsystem, a Program of Backup/Restore Control Indication thattransmits a Backup/Restore Control Indication to the storage subsystem,and a CPU that controls the application, Program of Volume Pair ControlIndication, and Program of Backup/Restore Control Indication.

The Disk Control Program receives the Program of Volume Pair ControlIndication from the host computer and performs the volume pair controlof the disk in response to the Volume Pair Control Indication. TheBackup/Restore Control Program receives the Backup/Restore ControlIndication from the host computer, performs the backup from the disk tothe tape and restoration from the tape to the disk in response to theBackup/Restore Control Indication, and at this time performs themanagement of backup data and backup differential data. The Tape LibraryControl Program receives a Tape Import Indication from the managementterminal, performs tape import in response to the Tape ImportIndication, and also receives a Tape Export Indication from themanagement terminal and performs tape export in response to the TapeExport Indication.

More specifically, the Disk Control Program can create a pair of aprimary volume and a secondary volume in the disk by the Volume PairControl Indication. The Disk Control Program can perform differentialdata management of the primary volume and secondary volume and canperform differential data copying or pair splitting according to theVolume Pair Control Indication. The Backup/Restore Control Program canperform backup data differential management, can performfull/differential/incremental backup of the pair-split secondary volumeto a tape according to the Backup Control Indication, and in the case ofdifferential/incremental backup at this time, can store on the tape notonly the data that are the object of backup but also the informationnecessary for restoration. The Backup/Restore Control Program canrecover data from the full/differential/incremental backup data that arestored in the tape to the pair-split secondary volume according to theRestore Control Indication, and in the case of restoration from thedifferential/incremental backup data at this time, can restore data byusing the information necessary for restoration that has been stored onthe tape. The Disk Control Program can copy the secondary volume forwhich data restoration has been performed to the primary volumeaccording to the Volume Pair Control Indication. Furthermore, datarestoration can be performed from the full/differential/incrementalbackup data that are stored on the tape even in the storage subsystemother than the storage subsystem where the backup has been performed.This is because the information necessary for restoration has beenrecorded on the tape. The Tape Library Control Program can export a tapefrom the storage subsystem according to the Tape Export Indication. TheTape Library Control Program can import a tape into the storagesubsystem according to the Tape Import Indication and also can restoredata from the imported tape.

The first embodiment will be described below in greater detail.

FIG. 1 shows an exemplary configuration of a computer system of thefirst embodiment of the present invention. FIG. 2 shows an exemplaryconfiguration of a controller 123 of the system shown in FIG. 1.

A host computer 100, a storage subsystem 101, and a management terminal103 are connected by using a fiber channel and can exchange informationand processing requests. The host computer 100, storage subsystem 101,and management terminal 103 may be connected by a communication networksuch as LAN (Local Area Network) or may be connected by a special lineor the like.

The host computer 100 comprises an application 111 that writesinformation to the storage subsystem 101 and reads informationtherefrom, a Program 112 of Volume Pair Control Indication that issues aVolume Pair Control Indication, a Program 113 of Backup/Restore ControlIndication that issues a Backup/Restore Control Indication, a memory 121for storing the application 111, Program 112 of Volume Pair ControlIndication and Program 113 of Backup/Restore Control Indication, and aCPU (Central Processing Unit) 122 for executing the application 111,Program 112 of Volume Pair Control Indication and Program 113 ofBackup/Restore Control Indication. The CPU 122 executing the Program 112of Volume Pair Control Indication issues a variety of commands such asPair Create Indication, Pair Re-synchronize Indication, Pair SplitIndication, and Pair Delete Indication. When a program is hereinbelow asubject, it actually means processing performed by the CPU executing theprogram. The Program 113 of Backup/Restore Control Indication issuesvarious commands such as Bull Backup Start Indication, DifferentialBackup Start Indication, Incremental Backup Start Indication, andRestore Start Indication.

The storage subsystem 101 comprises a controller 123, a plurality ofdisks 124, and a tape library device 125. The controller 123 comprises aProgram 131 of Backup/Restore Control that performs Management of BackupData, Processing of Backup, and Processing of Restore, a Disk ControlProgram 132 that performs Management of Data, Management of Volume Pair,Processing of Host I/O, and Processing of Volume Pair, and a TapeLibrary Control Program 133 that performs Management of Tape, Processingof Tape Import, and Processing of Tape Export.

The tape library device 125 comprises a plurality of tapes 136, a robot134 that transfers the tapes 136, a tape drive 135 that writesinformation on the tape 136 and reads information therefrom, and a tapeexport/import slot 137 for taking the tape 136 out of the storagesubsystem 101 and inserting the tape thereinto.

The Disk Control Program 132 has a function of creating a volume paircomposed of a primary volume 124 a and a secondary volume 124 b and alsohas functions of pair re-synchronizing that performs differential datacopying between the volumes, pair splitting that splits the volumes, andpair deletion that deletes a volume pair. The Disk Control Program 132comprises a program 214 for performing management of disk 124, a program215 for performing management of volume pair, a program 216 forprocessing I/O, e.g., writing and reading information from the hostcomputer 100, and a program 217 for processing a volume pair. The term“volume” as used herein stands for a logical volume, which is a logicalstorage device, more specifically, for a storage space portion that iscut out from a storage space provided by one or a plurality of disks 124(for example, two or more disks 124 constituting a RAID group). The“primary volume” is a logical volume of copy source, and the “secondaryvolume” is a logical volume of copy destination.

The Backup/Restore Control Program 131 includes a program 211 thatperforms management of backup data, a program 212 that performsprocessing of backup, and a program 213 that performs processing ofrestore. Management 211 of Backup Data has a function of managing backupdata and also has a function of managing differential data of backup forperforming differential/incremental backup. Furthermore, theBackup/Restore Control Program 131 has a function of performingfull/differential/incremental backup of information of the secondaryvolume 124 b on the tape 136 or restoring the information of tape 136 tothe secondary volume 124 b. It goes without saying, that the backupsource and restore destination may be the primary volume 124 a or thedisk 124 that does not constitute a volume pair.

The Tape Library Control Program 133 comprises a program 218 thatperforms management of tape 136, a program 219 that performs processingof tape import, and a program 220 that performs processing of tapeexport. The Tape Library Control Program 133 has a function of exportingthe tape 136 and a function of importing the tape by using the tapeexport/import slot 137.

The management terminal 102 includes a management screen 141 andperforms of managing the storage subsystem 101. For example, themanagement terminal creates a logical volume (referred to hereinbelow asLU) of the disk 124 and issues an Export/Import Indication of tape 136.The management screen 141 is, for example, a display screen of a displaydevice (not shown in the figure) of the management terminal 102.

The controller 123 comprises a memory (referred to hereinbelow as“control memory”) 201 for storing the Backup/Restore Control Program131, Disk Control Program 132, and Tape Library Control Program 133, aprocessor (for example, a CPU; referred to hereinbelow as “controlprocessor”) 202 for executing the Backup/Restore Control Program 131,Disk Control Program 132, and Tape Library Control Program 133, a cachememory 203 for storing information temporarily, and a data transfer LSI(Large Scale Integration) 204 for performing data transfer between thehost computer 101, disk 124, and tape library device 125.

FIG. 3 shows an example of management information held by the Management215 of Volume Pair.

For example, a Volume Pair Management Table 301, a Volume PairDifferential Management Table 302, and a Volume Pair DifferentialManagement Bitmap 303 are contained in the management information heldby the Management 215 of Volume Pair.

The Volume Pair Management Table 301 serves to manage the configurationinformation or status of a volume pair created by Processing 217 ofVolume Pair. In this Table 301, a volume pair number 311, a primaryvolume 312, a secondary volume 313, and a status 314 are recorded foreach volume pair. The volume pair number 311 is a number uniquelyidentifying a volume pair. The primary volume 312 is a LUN (logical unitnumber) of a LU (logical unit) serving as the primary volume 124 a. Thesecondary volume 313 is a LUN of a LU serving as the secondary volume124 b. The status 314 is the volume pair status such as a pair status, asplit status, a status of transition to a pair status, a status oftransition to a split status, or an error status. The pair status is astatus in which the information of the primary volume 124 a and theinformation of the secondary volume 124 b are synchronized. The splitstatus is a status in which the information of the primary volume 124 aand the information of the secondary volume 124 b are not synchronized.The status of transition to a pair status is a status in whichtransition processing is made to a pair status.

The Volume Pair Differential Management Table 302 serves to manage thedifference between the primary volume 124 a and secondary volume 124 bfor each volume pair. This difference is managed, for example, by aVolume Pair Differential Management Bitmap 303. In this Table 302, avolume pair number 321, a differential bitmap number 322, a differentialmanagement size 323, and a differential bitmap storage position 324 arerecorded for each volume pair. The volume pair number 321 indicateswhich volume pair has the differential bitmap. The differential bitmapnumber 322 is a number that uniquely identifies the Volume PairDifferential Management Bitmap 303. The differential management size 323indicates the size to which one bit of the differential bitmapcorresponds. The differential bitmap storage position 324 indicateswhere on the disk 124 the differential bitmap is stored. For example, ifthe differential bitmap storage position 324 is 0:0-0:1000, it indicatesthat the bitmap is stored from LBA 0 to 1000 in the LU with a LUN=0. Thebit map storage position may be stored on the control memory 201 orcache memory 203, rather than on the disk 124, to increase the referencerate.

For example, if the differential management size 323 is 1 MB, then 331 aindicates a differential bit of a block corresponding to 1 MB from thehead section of the LU, and 331 b indicates the differential bit of ablock corresponding to 2 MB from 1 MB of the head section of the LU. Thedifferential bit 331 is any one of the corresponding blocks, and if theinformation of the primary volume 124 a is different from that of thesecondary volume 124 b, the bit is inverted. For example, 331 a, 331 b,331 e indicate that the information of the primary volume 124 a and theinformation of the secondary volume 124 b match, and 331 c and 331 dindicate that the information of the primary volume 124 a and theinformation of the secondary volume 124 b do not match. The primaryvolume 124 a and secondary volume 124 b each have one differentialbitmap. As for the differential bit 331, if any one of the correspondingblocks is updated, the differential bit is inverted, and thedifferential data of the primary volume 124 a and secondary volume 124 bmay be managed by comparing the respective differential bitmaps. Thedifferential bitmap size is determined by the LU capacity anddifferential management size 323. For example, if the LU capacity is 100MB and the differential management size 323 is 1 MB, then the size ofone differential bitmap will be 100 bit.

FIG. 4 shows an example of logical image of a tape pool 401 managed byManagement 218 of Tape.

The tape pool 401 comprises a plurality of tapes 136, and some of thetapes 136 are grouped, constituting a tape group 411. There are alsotapes, such as a tape 136 j, that are not grouped into the tape group411. For example, a tape group 411 a is composed of a tape 136 a and atape 136 b. Half a tape, as in a tape 136 d, maybe used in a tape group411 b and the remaining half may be used in a tape group 411 c.Furthermore, the tape group 411 is not necessarily composed of two ormore tapes 136. For example, the tape group 411 may be also composed ofone tape 136 or part of the tape 136. In FIG. 4, a plurality of tapepools 401 are shown, all the tape pools 401 having the sameconfiguration. However, it goes without saying that each tape pool 401may have different configuration.

The tape pool 401 is created in the units of the tape library device 125by using the management terminal 102. The tape pool 401 is composed ofthe tapes 136 of the tape library device 125. The creation of the tapepool 401 may be conducted from the host computer 100. A plurality oftape pools 401 may be created in the tape library device 125, or thetape pool may be created for a plurality of tape library devices 125. Inbackup processing, the tape pool 401 is indicated as a backupdestination, and backup is successively conducted to the tape that isnot used. A plurality of backup source volumes may be indicated. Thetape that is used for backup may be a tape in which absolutely no datahave been recorded, that is, a completely unused tape. For example, inthe backup, data may be overwritten on the tape where data that requireno backup have been recorded, and the process may be continued to acertain point on the tape where the backup data have been recorded. Thetape group 411 is created by grouping the tapes used in the backup.Accordingly, the backup unit becomes a tape group 411, and themanagement of backup data is conducted in tape group units. The tapegroup 411 may be created by using the management terminal 102 or thelike prior to backup and the tape group 411 may be indicated as a backupdestination. The created tape group 411 has a function of adding, ifnecessary, a tape that does not constitute the tape group 411, such astape 136 j. For example, the tape group 411 a that is created in advanceis indicated as a backup destination, but when backup data have not yetbeen entered into the tape 136 a and tape 136 b, the backup dataremaining in the tape 136 j are stored, and the tape group 411 a isconstituted of tapes 136 a, 136 b, 136 j.

During the backup, a tape area (recording area of the entire or part ofone or a plurality of tapes 136) for constituting the tape group 411 maybe reserved in advance from the tape pool 411 based on the size of datathat are the backup object and the size of the management information(information including the information necessary for restoration) thatwill be stored together with the data and the backup may be conductedinto this reserved tape area, but constituting the tape group 411 whenthe backup has been completed, as in the present embodiment, is moreefficient. This is because, the size of data to be written into the tape136 is not known before the backup is completed. The primary factortherefore is that the data to be written into the tape 136 arecompressed by the function of the tape drive 135. In other words, thesize of data recorded on the tape 136 is actually less than the size ofdata sent as the write object to the tape drive 135. For this reason,even if the tape 136 is reserved in advance, the capacity can be toolarge or, conversely, insufficient. In the present embodiment, theoccurrence of such problem is avoided by constituting the tape group 411after the backup has been completed.

Furthermore, as shown in FIG. 4, a plurality of tape groups 411 arelinked into one tape pool 401, but when a plurality of backup operationsare conducted with respect to a certain backup source LU, those afterthe backup time are backed up at the position downstream of those beforethe backup time. For example, when differential backup is conductedafter the full backup, the differential backup may be performed from aposition downstream (for example, immediately thereafter) of the tapepool corresponding to the full backup. Furthermore, for example, whenincremental backup is performed after the differential backup, theincremental backup may be performed from a position downstream (forexample, immediately thereafter) of the tape pool corresponding to thisdifferential backup. Such an approach makes it possible to avoidfrequent forwarding and rewinding of the tape during the restoration.

FIG. 5 shows an example of storage information of the tape group 411.

The tape group 411 comprises tape group information 501 and backup data502. The backup data 502 comprise data management information 511 anddata 512. The tape group information 501 is management information ofthe tape group 411 that has to be restore processed.

The backup data 502 is backup data of the backup source LU. The datamanagement information 511 is management information of the backupsource LU that has to be restore processed. The data 512 is user's data(data used in the application 111 of the host computer 100) of thebackup source LU (secondary volume serving as a backup source). Thus,the “backup data” as referred to in the present embodiment can be acombination of user's data and data management information. The tapegroup information 501 and tape management information 511 will beexplained below with reference to FIGS. 8, 9 and 10.

FIG. 6 shows an example of management information of the Management 218of Tape.

The management information includes a Tape Pool Management Table 601, aTape Group Management Table 602, and a Tape Media Management Table 603.

The Tape Pool Management Table 601 is a table for managing the tape pool401. A tape pool number 611, a number 612 of the tape constituting thetape pool, and a storage tape group number 613 are recorded in the Table601. The tape pool number 611 is a number for uniquely identifying thetape pool 401. The tape number 612 is the number of the tapeconstituting the tape pool 401. The tape numbers may be recorded in thesequence of 101,102, 103, or the numbers 111-131 may be recorded toreduce the table capacity and the configuration may include tapes withthe numbers from the tape number 111 to the tape number 131.Furthermore, recording may be conducted by a combination of the formerand the latter. The storage tape group number 613 is the number of thetape group 411 that has been created in the tape pool 401. For example,the tape pool 401 with the tape pool number 1 is composed of tapes 136with the tape numbers 101,102,103, and the tape groups 411 with the tapegroup numbers 11, 12, 13 are created.

The Tape Group Management table 602 is a table for managing the tapegroup 411. A tape group number 621, a tape group status 622, tapes 623constituting the tape group, a backup source LUN 624, a backup dataclass 625, a tape group number 626 necessary for restoration, a number627 of the tape pool to which the tape group belongs, and the recordingdate and time 628 are recorded in the Table 602. The tape group number621 is a number for uniquely identifying the tape group 411. The tapegroup status 622 indicates the status of the tape group, such as“Normal”, “Backup is conducted”, “Restoration is conducted”, and“Error”. The tape group configuration tape 623 is informationrepresenting the position of the tape group (position information), andthis position information is represented, for example, by the tapenumber 631 and object address. 101:10-900 indicates the address from 10to 900 of the tape number 101. The backup source LUN 624 indicates theLUS of the backup source LU (backup source volume). The backup dataclass 625 indicates whether the data are the full backup data,differential backup data, or incremental backup data. The tape groupnumber 626 necessary for restoration indicates the tape group number 621that is necessary during the restoration. The tape pool number 627indicates the tape pool number 611 to which the tape group 411 belongs.The recording date and time 628 indicates date and time when the backupis started. The recording date and time 628 may record the backup enddate and time or the indicated date and time during the Processing ofBackup.

For example, it can be assumed that full backup is performed at 22:00:00of Apr. 4, 2006, differential backup is performed at 22:00:00 of Apr.11, 2006, and incremental backup is performed at 22:00:00 of Apr. 12,2006. In the tape group 411 of the tape group number 11, the LU of LUN2001 and 2002 are recorded at 22:00:00 of Apr. 4, 2006 and the fullbacked-up data are recorded in the tape numbers 101, 102, 103. In thetape group 411 of the tape group number 12, the LU of LUN 2001 and 2002are recorded at 22:00:00 of Apr. 11, 2006 and the differential backed-updata are recorded in the tape numbers 104, 105. In the tape group 411 ofthe tape group number 13, the LU of LUN 2001 and 2002 are recorded at22:00:00 of Apr. 12, 2006 and the incremental backed-up data arerecorded in the tape numbers 106. In order to perform Processing ofRestore from the full backed-up data of the tape group 411 of the tapegroup number 11, only the tape group 411 of the tape group number 11 maybe employed. Therefore, nothing is recorded in the tape group number 626necessary for restoration. In order to perform Processing of Restorefrom the differential backed-up data of the tape group 411 of the tapegroup number 12, the tape group 411 of the tape group number 11 is alsonecessary. Therefore, 11 is recorded in the tape group number 626necessary for restoration. In order to perform Processing of Restorefrom the incremental backed-up data of the tape group 411 of the tapegroup number 13, the tape groups 411 of the tape group numbers 11 and 12are also necessary. Therefore, 11 and 12 are recorded in the tape groupnumber 626 necessary for restoration. In this case, in the Processing ofRestore, the copy processing of the tape group 411 (copying from thetape to the restore destination volume) is conducted in the order totape group numbers of 11, 12, 13. If the tape group number 621 of thetape group 411 where the backup data of the previous cycle have beenrecorded is recorded in the tape group number 626 necessary forrestoration, for example, if a restore request is issued by indicatingthe tape group 411 of the tape group number 13, then the tape groupnumber 626 necessary to restore the tape group number 13 is referred to,thereby clarifying the necessity of conducting the copy processing ofthe tape group 411 of the tape group number 12 prior thereto, then thetape group number 626 necessary to restore the tape group number 12 isreferred to, thereby clarifying the necessity of conducting the copyprocessing of the tape group 411 of the tape group number 11 priorthereto, then the tape group number 626 necessary to restore the tapegroup number 11 is referred to, thereby clarifying that the tape groupnumber 621 is the full backup data, and the copy processing of the tapegroup 411 may be conducted in the order to tape group numbers of 11, 12,13.

The Tape Media Management Table 603 is a table for managing the tapes136. A tape number 631, a tape class 632, one block size 633, a tapecapacity 634, a used capacity 635, a tape status 636, a number 637 ofthe tape pool to which the tape belongs, and a number 638 of the tapegroup to which the tape belongs are recorded in the Table 603. The tapenumber 631 is a number for uniquely identifying the tape 136. The tapeclass 632 indicates a tape standard such as LTO3 or LTO4. One block size633 indicates the capacity of one block of the tape 136. The tapecapacity 634 indicates the capacity of tape 136. Used capacity 635indicates that backup data capacity that has been recorded in the tape136. The tape status 636 indicates the status of tape 136, such as“Normal”, “Not used”, and “Error”. For example, “Normal” indicates thestatus in which backup data have been recorded normally, “Not used”indicates the status in which the backup data have not been recorded,and “Error” indicates the status in which the tape 136 cannot be useddue to media failure or the like. The tape pool number 637 indicates thetape pool number 611 to which the tape 136 belongs. The tape groupnumber 638 indicates the tape group number 621 to which the tape 136belongs. For example, the tape 136 of the tape number 101 has the backupdata recorded therein and belongs to the tape pool 401 of the tape poolnumber 1 and to the tape group 411 of the tape group number 11. The tape136 of the tape number 111 has no backup data recorded therein andbelongs to the tape pool 401 of the tape pool number 4.

FIG. 7 shows as example of management information of the Management 211of Backup Data.

This management information includes a Backup Data Management Table 701,a Data Differential Management Table 702, and a Backup Data DifferentialManagement Bitmap 703.

The Backup Data Management Table 701 is a table for managing the backupdata. A backup data number 711, a backup source LUN 712, a backupdestination tape group number 713, a backup data status 714, a backupdata class 715, and a backup acquisition date and time 716 are recordedin this Table 701. The backup data number 711 is a number for uniquelyidentifying the backup data. The backup source LUN 712 indicates the LUNof the backup source LU. The backup destination tape group number 713indicates the tape group number 621 where the backup data have beenrecorded. The backup data status 714 indicates the status of backupdata, such as “Normal”, “Restore impossible”, and “Error”. For example,“Normal” represents a status in which the backup data can be recorded.“Restore impossible” indicates a status in which the backup data havebeen lost and restoration is impossible, but represents a status inwhich the tape 136 can be used. “Error” represents a status in which thetape 136 cannot be used due to a tape media failure. The backup dataclass 715 indicates the full backup data, differential backup data, orincremental backup data. The backup acquisition date and time 716indicates the date and time where the backup is started. In the backupacquisition date and time 716, the backup end date and time may berecorded or date and time indicated during Processing of Backup may berecorded.

The Data Differential Management Table 702 and Backup Data DifferentialManagement Bitmap 703 serve to perform data differential management forperforming differential/incremental backup. The differential datamanagement is performed by the differential bitmap for each backupsource LU. It goes without saying, that the differential data may bemanaged by other method, for example, with a differential data list,rather than with the differential bitmap. For example, in thefull/differential/incremental backup operation in which full backup isperformed at the beginning of each month, incremental backup isperformed on workdays, and differential backup is performed on Sundays,the differential backup and incremental backup cannot be combined withone differential bitmap. Therefore, two differential bitmaps fordifferential backup and incremental backup are provided for each backupsource LU.

LUN 721, a differential bitmap number 722, a backup class 723, adifferential management size 724, and a differential bitmap storageposition 725 are recorded in the Data Differential Management Table 702.The LUN 721 indicates a LUN of the LU where differential data managementis conducted (in other words, a secondary volume that is the object ofdifferential data management). The differential bitmap number 722 is anumber that uniquely identifies the Data Differential Management Bitmap703. The backup class 723 indicates whether the correspondingdifferential bitmap is for differential backup or for incrementalbackup. The differential management size 724 indicates the size to whichone bit of the differential bitmap corresponds. The differential bitmapstorage position 725 indicates where in the disk 124 the differentialbitmap has been stored. For example, if the differential bitmap storageposition 725 is 5:0-5:1000, it indicates that the differential bitmaphas been stored from LBA 0 to 1000 of the LU with a LUN of 5. Thestorage position of the differential bitmap may be on the control memory201 or on the cache memory 20, rather than on the disk 24, to acceleratethe reference rate.

In the Data Differential Management Bitmap 703, for example, if thedifferential management size 724 is 1 MB, then 731 a indicates adifferential bit of a block corresponding to 1 MB from the head sectionof the LU and 731 b—from 1 MB to 2 MB from the head section of the LU.If any one of the corresponding blocks has been updated, thedifferential bit is inverted. For example, in the presentrepresentation, 731 a, 731 b, 731 e have not been updated, 731 c, 731 dhave been updated, and during the differential/incremental backup, theblocks corresponding to 731 c, 731 d are the backup objects. At the timeof full backup end, the differential bitmaps for differential backup andincremental backup are reset. At the time of the differential backup andincremental backup end, only the differential backup for incrementalbackup is reset. The size of the differential bitmap is determined bythe capacity of LU and the differential management size 724. Forexample, if the LU capacity is 100 MB and the differential managementsize 724 is 1 MB, then the size of differential bitmap is 100 bit.

FIG. 8 shows an example of recording format of the tape 136. FIG. 9shows an example of management information to be recorded on the tapeduring full backup. FIG. 10 shows an example of management informationto be recorded on the tape during differential/incremental backup. Themanagement information to be recorded on the tape during backup recordsthe management information held by the control memory 201.

A plurality of blocks 811 and a plurality of EOD (End Of Data) 812 arerecorded on the tape. A block number identifying each block 811 isattached to the block 811, and the block number is a number that isincreased by 1 in the order of 1, 2, 3 . . . from the BOT (Beginning OfTape) of tape 136 to the EOT (End Of Tape) of tape 136. If a block 811is recorded on the tape 136 immediately after the tape 136 is mounted onthe tape drive 135, the block 811 is recorded where the block number is1, and if the next block 811 is recorded, then the block 811 is recordedwhere the block number is 2. If other blocks 811 are then recorded, theblocks 811 are recorded successively where the block number is 3, wherethe block number is 4, . . . , toward the EOT side. Furthermore, If theblock 811 is reproduced immediately after the tape 136 has been rewound,then the block 811 with the block number 1 is reproduced, and if thenext block 811 is reproduced, the block 811 is reproduced successivelytoward the EOT so that the block 811 with the block number 2 isreproduced. The reproduction of blocks 811 is conducted until thefinally recorded block 811 is reproduced.

The tape information 821 is recorded in the block number 1, which is thehead block of the tape 136A. The tape information 821 may be recorded ina plurality of blocks with block numbers 1, 2, and the like. During fullbackup and also during the differential/incremental backup, the tapenumber 631, tape class 632, one block size 633, and tape capacity 634are recorded as tape information 821, with reference to the Tape MediaManagement Table 603.

The tape group information 501 is recorded in the block number next tothe block where the tape information 821 is recorded. The tape groupinformation 501 may be recorded in a plurality of blocks. In the case offull backup, a device number 921, a tape group number 621, a backupsource LUN 624, a backup data class 625, and recording date and time 628are recorded as the tape group information 501, and in the case ofdifferential/incremental backup, a backup source device number 921, atape group number 621, a backup source LUN 624, a backup data class 625,recording date and time 628, and a data group number 626 necessary forrestoration are recorded as the tape group information by referring tothe Tape Group Management Table 602. The device number 921 is a numberfor uniquely identifying the storage subsystem 101 where the backup isconducted.

The data management information 511 is recorded in the block number nextto the block where the tape group information 501 has been recorded. Thedata management information 511 may be recorded in a plurality ofblocks. In the case of full backup, a LUN 931 and a LU capacity 932 arerecorded as the data management information 511, and in the case ofdifferential/incremental backup, the LUN 931, LU 932, differentialmanagement size 724, and differential bitmap 703 are recorded as thedata management information with reference to the Data DifferentialManagement Table 702. The LUN 931 is a LUN of the backup source LU. TheLU capacity 932 is a LU capacity of the backup source LU. In the case ofincremental backup, the differential bitmap 703 contained in the datamanagement information 511 is for incremental backup. Thus, in the caseof incremental backup, only the incremental bitmap is recorded on thetape (that is, for each single LU) and the differential bitmap may notbe recorded. A bit that is the differential backup object is recorded inthe differentia bitmap, and a bit that is an incremental backup objectis recorded in the incremental bitmap so that whether to performdifferential backup or to perform incremental backup can be determinedby the indication from the host computer 100.

Data of the backup source LU are recorded from the block number next tothe block where the data management information 511 is recorded. In theProcessing of Full Backup, all the data of the backup source LU arerecorded, and in the Processing of Incremental/Differential Backup, onlydifferential data are recorded. Once recording of the backup source LUof the data management information 511 a has ended, the recording of thebackup source LU of the data management information 511 b is performedin the block with the next block number. Recording of the datamanagement information 511 b may be performed in the block with theblock number next to the data management information 511 a, and the dataof all the LU of the backup source LU may be recorded in the block withthe lock number next to the data management information 511.

Once the recording of all the backup source LU has ended, the EOD 812 isrecorded, and recording on the tape in the Processing of Backup iscompleted. When the backup data are recorded on the same tape 136A, therecording to the tape is performed from the block with the block numbernext to the EOD 812. Furthermore, in the case where the backup data arerecorded on the tapes 136A and 136B, the tape information 821 isrecorded on the head block of the tape 136B, and the continuation ofinformation recorded in the final block of the tape 136A is recorded inthe block with the next block number.

FIG. 11 shows the processing flow executed when the storage subsystem101 receives a write request to the disk 124 from the host computer 100.

In step 1000, the controller 123 receives the write request to the disk124 from the host computer 100. As a result, the Disk Control Program132 is executed. By the Disk Control Program 132, the write object datacorresponding to the write request are temporarily stored in the cachememory 203.

In step 1010, the Disk Control Program 132 refers to the Volume PairManagement Table 301 and checks whether the LUN of the write estimationLU is a primary volume 312 or a secondary volume 313. If it is, theprocessing flow advances to step 1020, if it is not, the processing flowadvances to step 1040.

In step 1020, the Disk Control Program 132 refers to the status 314 ofthe Volume Pair Management Table 301 and the Volume Pair DifferentialManagement Bitmap 303 and checks whether the differential bit of thewrite object has to be inverted. When the differential bit has to beinverted (for example, in the case where it is determined that the writeobject data will be written in a location in which the differential bitis not inverted as the status is a pair split status), the processingflow advances to step 1030, and in the case where the incremental bitdoes not have to be inverted (for example, in the case of a pair statusor when the status is a pair split status, but the differential bit hasalready been inverted), the processing flow advances to step 1040.

In step 1030, the Disk Control Program 132 inverts the differential bitthat is the write object of the Volume Pair Differential ManagementBitmap 303.

In step 1040, the Backup/Restore Control Program 131 refers to theBackup Data Differential Management Table 702 and checks whether the LUNof the write destination LU is LUN 721. If it is, the processing flowadvances to step 1050, if it is not, the processing flow advances tostep 1070.

In step 1050, the Backup/Restore Control Program 131 refers to theBackup Data Differential Management Bitmap 703 and checks whether thedifferential bit that is a write object has already been inverted. Ifthere are differential bitmaps for both the differential backup and theincremental backup, both bitmaps are checked. When the bit has beeninverted, the processing flow advances to step 1070, and when the bithas not been inverted, the processing flow advances to step 1060.

In step 1060, the Backup/Restore Control Program 131 inverts thedifferential bit of the write object of the Backup Data DifferentialManagement Bitmap 703. If there are differential bitmaps for both thedifferential backup and the incremental backup, the differential bits ofboth bitmaps are inverted.

In step 1070, the Disk Control Program 132 writes the data that aretemporarily stored in the cache memory 203 into the disk 124. In step1080, the Disk Control Program 132 sends a completion report to the hostcomputer 100.

FIGS. 12 and 13 show the processing flow of Processing of Full Backup,FIGS. 12 and 14 show the processing flow of Processing of DifferentialBackup, and FIGS. 12 and 15 show the processing flow of Processing ofIncremental Backup.

In step 2000, it is checked whether the LU that is wished to be backedup forms a volume pair. This may be checked by the user, or the Program112 of Volume Pair Control Indication may check the Volume PairManagement Table 301. In the case where a pair has not been created, theprocessing flow advances to step 2010, and in the case where a pair hasbeen created, the processing flow advances to step 2040.

In step 2010, a Pair Create Indication is issued from the Program 112 ofVolume Pair Control Indication of the host computer 100 to the storagesubsystem 101. In step 2020, the Disk Control Program 132 receives thePair Control Indication. In step 2030, the Disk Control Program 132updates the Volume Pair Management Table 301, Volume Pair DifferentialManagement Table 302, and Volume Pair Differential Management Bitmap303, copies the information of the primary volume 124 a to the secondaryvolume 124 b, and sets the status 314 of the Volume Pair ManagementTable 301 to a pair status once the copying is completed.

In step 2040, a Pair Re-synchronize (Usual) Indication is issued fromthe Program 112 of Volume Pair Control Indication of the host computer100 to the storage subsystem 101. In step 2050, the Disk Control Program132 receives the Pair Re-synchronize (Usual) Indication. In step 2060,the Processing of Pair Re-synchronize (Usual) is performed. Thisprocessing is explained below with reference to FIG. 19.

In step 2070, a Pair Split Indication is issued from the Program 112 ofVolume Pair Control Indication of the host computer 100 to the storagesubsystem 101. In step 2080, the Disk Control Program 132 receives thePair Split Indication. In step 2090, the Processing of Pair Split isperformed. This processing is explained below with reference to FIG. 20.In the Pair Split Indication, a pair number is indicated for which theaforementioned LU that is wished to be backed up (in other words, thebackup source LU) becomes the secondary volume.

As shown in FIG. 13, in step 3000, a Full Backup Start Indication isissued from the Program 113 of Backup/Restore Control Indication of thehost computer 100 to the storage subsystem 101. In this Full BackupStart Indication, the LUN of the secondary volume in a volume paircorresponding to the pair number indicated by the Pair Split Indicationis indicated as the backup source LUN.

In step 3010, the Backup/Restore Control Program 131 receives the FullBackup Start Indication. At this timing, the Backup/Restore ControlProgram 131 may output a write prohibition request to the Disk ControlProgram 132. The same can be done in step 4000 and step 5000.

In step 3020, the Backup/Restore Control Program 131 checks whether aLUN of the backup source LU (for example, the backup source LUNindicated by the Full Backup Start Indication) is present in the LUN 721of the Backup Data Differential Management Table 702. When it is notpresent, the processing flow advances to step 3030, and when it ispresent, the processing flow advances to step 3040.

In step 3030, the Backup/Restore Control Program 131 starts backup datadifferential management of the backup source LU. The size of thedifferential bitmap is computed from the LU capacity (volume capacity)of the backup source LU and the differential management size 724, andthe differential bitmap storage position is reserved. The differentialmanagement size 724 may be determined in advance by the storagesubsystem 101 or may be set by the user. The Backup/Restore ControlProgram 131 creates two differential bitmaps for differential backup andincremental backup and enters the storage positions thereof into theBackup Data Differential Management Table 702.

In step 3040, the Disk Control Program 132 inhibits writing to thebackup source LU at the predetermined time (for example, when a writeprohibition request is received from the Backup/Restore Control Program131). More specifically, for example, the Disk Control Program 132 doesnot return the predetermined response (for example, write completionreport) even if the write request is received. The same can be done instep 4020 and step 5020.

In step 3050, the Tape Library Control Program 133 controls the robot134 and mounts the tape 136 serving as a backup destination on the tapedriver 135. At this time, the necessary tapes 136 may be mounted on aplurality of tape drives 135 and parallel writing may be performed, andcopy processing may be performed by replacing the tape 136 for whichcopying has ended with the tape 136 for which copying has not ended. Forexample, the tape 136 serving as a backup destination is an unused tapethat is randomly selected by the Tape Library Control Program 133. Thesame can be done in step 4030 and step 5030.

In step 3060, the Backup/Restore Control Program 131 and Tape LibraryControl Program 133 operate together, whereby the management information901 for recording on the tape during full backup is created and thecreated management information 901 is recorded on the tape 136. Forexample, the management information 901 can be created by processingsuch as referring to the control memory 201 and acquiring theinformation corresponding to the tape number 631 of the mounted tape 136from the Tape Media Management Table 603. The tape group number 621contained in the management information 901 is the number of the tapegroup for including at least one full backup data that will be recordedin the present Full Backup Start Indication. The LUN 931 and LU capacity932 are the LUN and LU capacity of the backup source LU in this fullbackup. For example, in the case where the present tape group is startedfrom the intermediate point of tape 136, but does not extend to theother tape 136, it is not necessary to create the tape information 821.This is because the tape information 821, as shown in FIG. 8, isinformation that will be recorded in the head section of the tape 136.This can be also done in step 4040 and step 5040.

In step 3070, the Backup/Restore Control Program 131, Disk ControlProgram 132, and Tape Library Control Program 133 operate together,whereby all the data of the LU indicated as the backup source are copiedfrom the disk 124 to the tape 136. In this full backup, for example, 14is recorded as the tape group number 621 in the Tape Group ManagementTable 602 shown in FIG. 6 by the Tape Management 218 and also “Backup isPerformed” is recorded as the tape group status 622, “Full” is recordedas the backup data class 625, and “Normal” is recorded as a tape groupstatus 622 when the backup is completed.

In step 3080, the Backup/Restore Control Program 131, Disk ControlProgram 132, and Tape Library Control Program 133 operate together,whereby step 3060 and step 3070 are repeated until copying of all the LUindicated as the backup source is completed. In step 3060 of thisrepetition, only the data management information 511 is created andrecorded. The data management information 511 is to be included in eachbackup data. The same can be done in step 4040 based on repeating step4060 and also in step 5040 based on repeating step 5060.

In step 3090, the management information of Management 211 of BackupData and Tape Management 218 is updated. For example, the Management 211of Backup Data adds information relating to the backup data subjected tofull backup to the Backup Data Management Tale 701. Furthermore, theTape Management 218 adds (or updates information in the case it hasalready been entered) relating to the tape group 411 to the Tape GroupManagement Table 602 and adds the number of the tape group for recordingthe present full backup data to the storage tape group number 613 of thetape pool management table 601. In the brackets above, for example, thecase in which the tape group has been defined in advance prior to thebackup is present as the case for information update (this is norrelated to the difference between full/differential/incremental). Inthis case, for example, when 621,622,627 are entered prior to the backupand 622,623,624,625,626,628 are entered (updated) after the backup, theinformation is sometimes updated in the Tape Group Management Table 602.

In step 3100, the Tape Library Control Program 133 controls the robot134 and unmounts the tape 136 from the tape driver 135. At this time,the Tape Library Control Program 133 may output a write permissionrequest to the Disk Control Program 132. The same can be done in step4080 or step 5080.

In step 3110, the Disk Control Program 132 permits writing to the backupsource LU at the prescribed moment (for example, when the writepermission request is received from the Tape Library Control Program133). The same can be done in step 4090 or step 5090.

In step 3120, the Backup/Restore Control Program 131 resets the BackupData Differential Management Bitmap 703 of the backup source LU of theManagement 211 of Backup Data for both the differential backup and forthe incremental back (for example, all differential bitmaps are set to0). In step 3130, the Backup/Restore Control Program 131 notifies thehost computer 100 of the backup processing end.

As shown in FIG. 14, in step 4000, a Differential Backup StartIndication is issued from the Program 113 of Backup/Restore ControlIndication of the host computer 100 to the storage subsystem 101. Withthis Differential Backup Start Indication, for example, the LUN of thesecondary volume in the volume pair corresponding to the pair numberindicated by the Pair Split Indication is indicated as a backup sourceLUN.

In step 4010, the Backup/Restore Control Program 131 receives theDifferential Backup Processing Start Indication. In step 4020, the DiskControl Program 132 prohibits writing to the backup source LU. In step4030, the Tape Library Control Program 133 mounts the tape 136 that is abackup destination on the tape drive 135. At this time, the necessarytapes 136 may be mounted on a plurality of tape drives 135 and parallelwriting may be performed, and copy processing may be performed byreplacing the tape 136 for which copying has ended with the tape 136 forwhich copying has not ended.

In step 4040, the Backup/Restore Control Program 131 and Tape LibraryControl Program 133 operate together, whereby management information 902for recording on a tape during differential backup is created and thismanagement information 902 is recorded on the tape 136. The tape groupnumber 621 is a present tape group number for including at least onedifferential backup data that will be recorded by the presentDifferential Backup Start Indication. The management information 902includes the tape group number 626 necessary for restoration, and thisnumber 626 is acquired, for example, from a backup destination tapegroup number 713 for which the Backup Data Management Table 701satisfies the following three conditions:

A LUN identical to the backup source LUN of the present differentialbackup is a backup source LUN 712.

The backup data class 715 is full.

The date and time that are the closest to the present date and time,from the backup acquisition date and time 716 satisfying (1) and (2).

Furthermore, the data management information 511 includes theDifferential Management Bitmap 703 at the differential management size724 corresponding to the LUN 721 of the backup source LUN or at thedifferential bitmap storage position 725 corresponding to this LUN 721.In the case of incremental backup for example, in the tape group number626 necessary for restoration that has been entered in the tape groupnumber (can be any of full/differential/incremental) that satisfies theconditions (1) and (3) above, a tape group number (for example, aplurality thereof is entered that has this tape group number (satisfiesthe conditions (1) and (3) above) added thereto.

In step 4050, the Backup/Restore Control Program 131, Disk ControlProgram 132, and Tape Library Control Program 133 operate together,whereby the data with inverted differential bit are copied from the disk124 to the tape 136 with reference to the Differential Management Bitmap703 located in the differential bitmap storage position 725 for whichthe LUN number 721 is a backup source LUN and the backup class 723corresponds to differential. In the course of this differential backup,for example, the present tape group number is recorded as the tape groupnumber 621 in the Tape Group Management Table 602 of FIG. 6 byManagement 218 of Tape, the “Backup is conducted” is recorded as thetape group status 622, “Differential” is recorded as the backup dataclass 625, and when the backup ends, “Normal” is recorded as the tapegroup status 622.

In the step 4060, the Backup/Restore Control Program 131, Disk ControlProgram 132, and Tape Library Control Program 133 operate together,whereby step 4040 and step 4050 are repeated until copying of all the LUindicated as the backup sources is completed.

In step 4070, the management information of the Management 211 of BackupData and Management 218 of Tape is updated. For example, the Management211 of Backup Data adds information relating to differential backup datato the Backup Data Management Table 701. The Management 218 of Tape addsinformation relating to a new tape group 411 where the differentialbackup data are recorded to the Tape Group Management Table 602 (orupdates information when the information has already been entered) andadds the number of the new tape group 411 to the storage tape groupnumber 613 of the Tape Pool Management Table 601.

In step 4080, the Tape Library Control Program 133 controls the robot134 and unmounts the tape 136 from the tape drive 135. In step 4090, theDisk Control Program 132 permits writing to the backup source LU. Instep 4100, the Backup/Restore Control Program 131 resets the Backup DataDifferential Management Bitmap 703 of the backup source LU for theincremental backup (for example, all the differential bitmaps are set to0). In step 4110, the Backup/Restore Control Program 131 notifies thehost computer 100 of the differential backup processing end.

As shown in FIG. 15, in step 5000, an Incremental Backup StartIndication is issued from the Program 113 of Backup/Restore ControlIndication of the host computer 100 to the storage subsystem 101.

In step 5010, the Backup/Restore Control Program 131 receives theIncremental Backup Start Indication. In step 5020, the Disk ControlProgram 132 prohibits writing to the backup source LU. In Step 5030, theTape Library Control Program 133 mounts the tape 136 serving as a backupdestination on the tape driver 135. At this time, the necessary tapes136 may be mounted on a plurality of tape drives 135, writing may beperformed in parallel, and copy processing may be performed by replacingthe tape 136 for which copying has ended with the tape 136 for whichcopying has not ended.

In step 5040, the Backup/Restore Control Program 131 and Tape LibraryControl Program 133 operate together, whereby management information 902for recording on a tape during incremental backup is created, and thismanagement information 902 is recorded on the tape 136. The tape groupnumber 621 is a present tape group number for including at least oneincremental backup data that will be recorded by the present IncrementalBackup Start Indication.

In step 5050, the Backup/Restore Control Program 131, Disk ControlProgram 132, and Tape Library Control Program 133 operate together,whereby the data with inverted differential bit are copied from the disk124 to the tape 136 with reference to the Differential Management Bitmap703 located in the differential bitmap storage position 725 for whichthe LUN 721 is a backup source LUN and the backup class 723 correspondsto incremental. In the course of this incremental backup, for example,the present tape group number is recorded as the tape group number 621in the Tape Group Management Table 602 of FIG. 6 by Management 218 ofTape, the “Backup is conducted” is recorded as the tape group status622, “Incremental” is recorded as the backup data class 625, and whenthe backup ends, “Normal” is recorded as the tape group status 622.

In the step 5060, the Backup/Restore Control Program 131, Disk ControlProgram 132, and Tape Library Control Program 133 operate together,whereby step 5040 and step 5050 are repeated until copying of all the LUindicated as the backup sources is completed.

In step 5070, the management information of the Management 211 of BackupData and Management 218 of Tape is updated. For example, the Management211 of Backup Data adds information relating to incremental backup datato the Backup Data Management Table 701. The Management 218 of Tape addsinformation relating to a new tape group 411 where the incrementalbackup data are recorded to the Tape Group Management Table 602 (orupdates information when the information has already been entered) andadds the number of the new tape group 411 to the storage tape groupnumber 613 of the Tape Pool Management Table 601.

In step 5080, the Tape Library Control Program 133 controls the robot134 and unmounts the tape 136 from the tape drive 135. In step 5090, theDisk Control Program 132 permits writing to the backup source LU. Instep 5100, the Backup/Restore Control Program 131 resets the Backup DataDifferential Management Bitmap 703 of the backup source LU of theManagement 211 of Backup Data for the incremental backup (for example,all the differential bitmaps are set to 0). In step 5110, theBackup/Restore Control Program 131 notifies the host computer 100 of theincremental backup processing end.

FIGS. 16, 17, and 18 show the processing flow of restore processing.

As shown in FIG. 16, in step 6010, the user or Program 112 of VolumePair Control Indication refers to the Volume Pair Management Table 301of the Management 215 of Volume Pair and checks whether the status 3145of the LU that is wished to be restored (restore destination LU, forexample, LU called on by the user) is a pair status. If it is a pairstatus, the processing flow advances to step 6020, and if it is not thepair status, the processing flow advances to step 7000.

In Step 6020, a Pair Split Indication is issued from the Program 112 ofVolume Pair Control Indication of the host computer 100 to the storagesubsystem 101. In step 6030, the Disk Control Program 132 receives thePair Split Indication. In step 6040, the pair split processing isperformed. Details thereof are described below in FIG. 20.

As shown in FIG. 17, in step 7000, a Restore Start Indication is issuedfrom the Program 113 of Backup/Restore Control Indication of the hostcomputer 100 to the storage subsystem 101

In step 7010, the Backup/Restore Control Program 131 receives theRestore Start Indication. At this time, the Backup/Restore ControlProgram 131 may issue a write prohibition request to the Disk ControlProgram 132.

In step 7020, the Disk Control Program 132 prohibits writing from thehost computer 100 to the restore destination LU at the prescribed time(for example, when the write prohibition request is received by theBackup/Restore Control Program 131).

In step 7030, the Backup/Restore Control Program 131 and the TapeLibrary Control Program 133 operate together, whereby a tape groupnumber 626 necessary for restoration the Tape Group Management Table 602of the tape group 411 indicated as a restore source is referred to andthe tape 136 where the full-backup data have been recorded is mounted onthe tape drive 135. For example, if nothing is recorded in the tapegroup number 626 necessary for restoring, then the tape group 411indicated as the restore source is full backup data, and if 11, 12 isrecorded in the tape group number 626 necessary for restoring, then thetape group 411 of the tape group number 11 which is a leading number isthe full backup data. Furthermore, for example, when the Backup/RestoreControl Program 131 receives the indication of backup acquisition dateand time of the backup data that are whished to be restored, then thetape group 411 of the backup destination tape group number 713corresponding to this backup acquisition date and time is theaforementioned “tape group 411 indicated as the restore source”.

In step 7040, the Backup/Restore Control Program 131, 132 and TapeLibrary Control Program 133 operate together, whereby data 512 presentin the full backup data are copied from the tape 136 where the fullbackup data have been recorded into the disk 124 of the LU indicated asthe restore destination. If the restore destination LU is notspecifically indicated, then it may be automatically considered as theLU that is the backup source.

In step 7050, the Tape Library Control Program 133 unmounts the tape 136where the full backup data have been recorded from the tape driver 135.

In step 7060, the Backup/Restore Control Program 131 refers to thebackup data class 625 corresponding to the date group 411 indicated as arestore source and checks whether the data is full backup data. In thecase of full backup data, the processing flow advances to step 7110, andin the case of differential backup data or incremental backup data, theprocessing flow advances to step 7070.

In step 7070, the Backup/Restore Control Program 131 and Tape LibraryControl Program 133 operate together, whereby the tape group number 626necessary for the restoration corresponding to the tape group 411indicated as a restore source is referred to and then the tape 136having recorded thereon the differential/incremental backup data(differential backup data or incremental backup data) that have to becopied is mounted on the tape drive 135. For example, if 21, 22 and 23are recorded in the tape group number 626 necessary for restoration,when copying of the tape group 411 with a tape group number of 21 iscompleted, copying of the tape group 411 with the tape group number of22 is then conducted, and when the copying of the tape group 411 withthe tape group number 22 is completed, copying of the tape group 411with the tape group number 23 is then conducted.

In step 7080, the Backup/Restore Control Program 131, Dick ControlProgram 132, and Tape Library Control Program 133 operate together,whereby the management information 902 located in the tape 136 where thedifferential/incremental backup data have been recorded is referred to,and the data 512 of the tape 136 are copied into the disk 124 with theLU indicated as a restore destination, while computing the LBA of therestore destination LU into which data 512 have to be copied. Forexample, the LBA of the restore destination LU into which data 512 haveto be copied is computed by using the differential bitmap 703 anddifferential management size 724 recorded on the tape 136. Morespecifically, for example, when the head section LBA of the restoredestination LU is 100, the block size is 1 MP, the differentialmanagement size 724 is 1 MB, and the differential bitmap 703 is taken as011001 from the head section, the computation is conducted as follows:the LBA of the restore destination LU where the leading data 512recorded on the tape 136 have to be copied is 101, the LBA of therestore destination LU where the second data 512 have to be copied is102, the LBA of the restore destination LU where the third data 512 haveto be copied is 105 . . . .

In step 7090, the Tape Library Control Program 133 unmounts from thetape drive 135 the tape 136 having recorded thereon thedifferential/incremental backup data for which the copying processinghas ended.

In step 7100, steps 7070, 7080, 7090 are repeated until all the tapegroup numbers 621 recorded in the tape group number 626 necessary forthe restoration are copied. In step 7110, the Backup/Restore ControlProgram 131 notifies the host computer 100 of the restore processingend.

As shown in FIG. 18, in step 8000, a Pair Re-synchronizing (Inversion)Indication is issued from the Program 112 of Volume Pair ControlIndication of the host computer 100 to the storage subsystem 101. Instep 8010, the Disk Control Program 132 receives the PairRe-synchronizing (Inversion) Indication. In step 8020, the Disk ControlProgram 132 performs the Processing of Pair Re-synchronizing(Inversion). For example, data are copied from the secondary volume 124b where the backup data recorded on the tape 136 are copied into theprimary volume 124 a and the data are matched.

Thus, the “Pair Re-synchronizing (Inversion) Indication” is anindication to set the volume pair with a pair split status into a statusof transition to a pair status and perform copying in the inverteddirection, while the volume pair is in this status. More specifically,this is an indication to match the contents of the secondary volume withthe contents of the primary volume by copying the data located in thesecondary volume (all the data, or the data representing the differencewith the primary volume) into the primary volume. By contrast, the “PairRe-synchronizing (Usual) Indication” is an indication to set the volumepair with a pair split status into a status of transition to a pairstatus and perform copying in the usual direction, while the volume pairis in this status. More specifically, this is an indication to match thecontents of the primary volume with the contents of the secondary volumeby copying the data located in the primary volume (all the data, or thedata representing the difference with the primary volume) into thesecondary volume.

FIG. 19 shows a processing flow of the Processing of PairRe-synchronizing (Usual).

In step 9000, the Management 215 of Volume Pair sets the status 314 ofthe Volume Pair Management Table 301 to a status of transition to a pairstatus.

In step 9010, the Disk Control Program 132 refers to the Volume PairDifferential Management Bitmap 303 of the Management 215 of Volume Pairand copies the differential data from the primary volume 124 a to thesecondary volume 124 b.

In step 9020, the Management 211 of Backup Data refers to the LUN 721 ofthe Backup Data Differential Management Table 702 and checks thepresence of a LUN of the secondary volume 124 b. When it is not present,the processing flow advances to step 9050, and when it is present theprocessing flow advances to step 9030.

In step 9030, the Management 211 of Backup Data refers to the BackupData Differential Management Bitmap 703 and checks whether thedifferential bit that is the object of copying has already beeninverted. The differential bitmaps for both the differential backup andthe incremental backup are checked. In the case where the differentialbit has been inverted, the processing flow advances to step 9050, and inthe case where the differential bit has not been inverted, theprocessing flow advances to step 9040.

In step 9040 the Management 211 of Backup Data inverts the differentialbit that is the copy object of the Backup Data Differential ManagementBitmap 703. The differential bits of the differential bitmaps for boththe differential backup and the incremental backup are inverted.

In step 9050, steps 9010, 9020, 9030, 9040 are repeated until the dataof the primary volume 124 a and secondary volume 124 b are matched.

In step 9060, the Management 215 of Volume Pair sets the status 314 ofthe Volume Pair Management Table 301 to a pair status.

FIG. 20 shows the processing flow of Processing of Pair Split.

In step 9100, the Management 215 of Volume Pair sets the status 314 ofthe Volume Pair Management Table 301 to a status of transition to a pairsplit status.

In step 9110, the Disk Control Program 132 refers to the Volume PairDifferential Management Bitmap 303 of the Management 215 of Volume Pairand, if the inverted bit is present, copies the differential datacorresponding to this bit from the primary volume 124 a to the secondaryvolume 124 b. The case where an asynchronous copying is conductedbetween the primary volume 124 a and secondary volume 124 b is anexample of the case where an inverted bit is present at this time.

In step 9120, the Management 211 of Backup Data refers to the LUN 721 ofthe Backup Data Differential Management Table 702 and checks whether aLUN of the secondary volume 124 b is present. When it is not present,the processing flow advances to step 9150, and when it is present theprocessing flow advances to step 9130.

In step 9130, the Management 211 of Backup Data refers to the BackupData Differential Management Bitmap 703 and checks whether thedifferential bit that is the object of copying has already beeninverted. The differential bitmaps for both the differential backup andthe incremental backup are checked. In the case where the differentialbit has been inverted, the processing flow advances to step 9150, and inthe case where the differential bit has not been inverted, theprocessing flow advances to step 9140.

In step 9140, the Management 211 of Backup Data inverts the differentialbit that is the copy object of the Backup Data Differential ManagementBitmap 703. The differential bits of the differential bitmaps for boththe differential backup and the incremental backup are inverted.

In step 9150, steps 9110, 9120, 9130, 9140 are repeated until the dataof the secondary volume 124 b match the data of the primary volume 124 aat the point in time the Pair Split Indication is received.

In step 9160, the Management 215 of Volume Pair sets the status 314 ofthe Volume Pair Management Table 301 to a split status.

With the above-described first embodiment, in the case ofdifferential/incremental backup of user's data, the managementinformation 902 is recorded in addition to the user's data on the tape136. As a result, when restoration is preformed, the restoration can beconducted by using the management information 902 recorded on the tape136, even when information of the control memory 201 of the storagesubsystem 101 where the backup is conducted is absent.

Furthermore, with the above-described first embodiment, the Backup DataDifferential Management Bitmap 703 is recorded on the tape 136 each timethe differential/incremental backup is performed. Further, when thedifferential backup is performed, the Differential Management Bitmaps703 for both the differential backup and the incremental backup arereset, and when the incremental backup is performed, the DifferentialManagement Bitmap 703 for the incremental backup is reset. In otherwords, the differential bitmaps that have to be held in the storagesubsystem for one or many backup source LU are two bitmaps for thedifferential backup and incremental backup, regardless of the number ofgenerations that have to be differentially managed. As a result, it ispossible to avoid limiting the number of generations that can bedifferentially managed to the storage capacity of the storage subsystemmemory.

Embodiment 2

For example, the primary volume 124 a may be allocated in the firststorage subsystem, the secondary volume 124 b may be allocated in thesecond storage subsystem, and remote copying may be performed betweenthe first and second storage subsystems. In this case, the tape librarydevice 125 is provided in the second storage subsystem.

Several preferred embodiments of the present invention are describedabove, but they merely serve to illustrate the present invention, andthe scope of the present invention is not limited to those embodiments.The present invention can be also implemented in a variety of otherforms.

1. A storage system comprising a plurality of storage devices of asequential access type, the storage devices operable to process asequential access at a high speed, but unable to process a random accessat a high speed, and at least one storage device of a random access typeoperable to process a random access faster than said storage devices ofa sequential access type, and in which data located in a logical volumeon said at least one storage device of a random access type are backedup in said storage devices of a sequential access type, said storagesystem comprising: a full backup section operable to execute a fullbackup causing all data located in said logical volume to be backed upfrom said logical volume to a sequential device group comprising saidplurality of storage devices of a sequential access type; a differentialmanagement information storage section operable to store differentialmanagement information, the differential management information beinginformation representing a difference between said logical volume andsaid sequential device group after said full backup; a differentialmanagement section operable to updates said differential managementinformation in response to an update of said logical volume; and apartial backup section operable to execute a partial backup by whichpartial data that are data equivalent to a difference between saidlogical volume and said sequential device group are specified by usingsaid updated differential management information, information necessaryfor restoration that is necessary to restore a data group located insaid updated logical volume by using said partial data is recorded insaid sequential device group, and said partial data are backed up fromsaid updated logical volume to said sequential device group, and furthercomprising: a backup management storage section operable to store backupunit management information representing, as a backup unit, a storagearea of said sequential device group, that has been consumed by a backupto said sequential device group, and a backup unit management sectionoperable to add, to said backup unit management information, informationrepresenting, as one backup unit, the storage area that has beenconsumed by said backup when said full backup or said partial backup iscompleted, wherein said backup unit management section comprises, foreach backup unit, a backup unit identifier, a backup class representinga class of backup, and a sequence information representing a sequence ofbackup in said backup unit management information, and said partialbackup section is operable to specify a backup unit having recordedtherein backup of data necessary for restoration of said partial backupbased on the sequence information and backup class in said backup unitmanagement information and comprises a backup unit identifier of saidspecified backup unit and a backup class indicating that this is apartial backup in said information necessary for restoration.
 2. Thestorage system according to claim 1, wherein: said partial backupsection includes said updated differential management information insaid information necessary for restoration, and said differentialmanagement section resets said updated differential managementinformation in the case where said partial backup is conducted, andupdates said reset differential management information in the case wheresaid logical volume is thereafter updated.
 3. The storage systemaccording to claim 1, wherein: said differential management informationis a bit map, each bit of said bit map corresponds to each volumeportion of said logical volume, and said partial backup section includesa storage size of said volume portion corresponding to the bit of saidbit map and a storage capacity of said logical volume in saidinformation necessary for restoration.
 4. The storage system accordingto claim 1, wherein: said at least one storage device of a random accesstype comprises a plurality of logical volumes, said partial backupsection is operable to performs said partial backup with respect to eachof said plurality of logical volumes, and said backup unit managementsection is operable to take a storage area comprising each data that isrecorded by each said partial backup as said backup unit.
 5. The storagesystem according to claim 1, wherein: said partial backup section isoperable to record said information necessary for restoration on theupstream side of said sequential device group from said partial data. 6.The storage system according to claim 1, wherein: said partial backupsection is operable to record said information necessary for restorationand said partial data on the downstream side from said all data that arerecorded by said full backup.
 7. The storage system according to claim1, further comprising: a restore section operable to restore saidupdated logical volume by using said information necessary forrestoration that is recorded in said sequential device group.
 8. Thestorage system according to claim 7, wherein: said differentialmanagement information is a bit map, each bit of said bit mapcorresponds to each volume portion of said logical volume, said partialbackup section comprises a storage size of said volume portioncorresponding to the bit of said bit map and a storage capacity of saidlogical volume in said information necessary for restoration, and saidrestore section is operable to restore said updated logical volume basedon said storage size and said storage capacity contained in saidinformation necessary for restoration.
 9. The storage system accordingto claim 1, wherein: said logical volume is a secondary logical volumefrom a volume pair comprising a primary logical volume, which is a copysource, and said secondary logical volume, which is a copy address. 10.The storage system according to claim 1, wherein: said partial backup isany one of a differential backup and an incremental backup.
 11. Thestorage system according to claim 1, wherein: said differentialmanagement information is a bit map, each bit of said bit mapcorresponds to each volume portion of said logical volume, said partialbackup section comprises, in said information necessary for restoration,said updated bit map, a storage size of said volume portioncorresponding to the bit of said bit map, and a storage capacity of saidlogical volume, records said information necessary for restoration andsaid partial data on the downstream side from said all data that arerecorded by said full backup, and at this time records said informationnecessary for restoration on the upstream side of said sequential devicegroup from said partial data, said differential management section isoperable to reset said updated bit map in the case where said partialbackup is conducted and updates said reset bit map in the case wheresaid logical volume is thereafter updated, and said partial backup isany one of a differential backup and an incremental backup.
 12. Thestorage system according to claim 11, wherein: said bit map comprises abit map for a differential backup and a bit map for an incrementalbackup, and said bit map for incremental backup is included into saidinformation necessary for restoration in the case of said incrementalbackup.
 13. A backup method for performing backup of data located in alogical volume on at least one storage device of a random access type toa storage device of a sequential access type in a storage system havinga plurality of said storage devices of a sequential access type that arestorage devices of a type that can process a sequential access at a highspeed, but cannot process a random access at a high speed, and said atleast one storage device of a random access type that is a storagedevice of a type that can process a random access faster than saidstorage devices of a sequential access type, said method comprising:executing a full backup by which all data located in said logical volumeare backed up from said logical volume to a sequential device groupcomprising said plurality of storage devices of a sequential accesstype; updating differential management information representing adifference between said logical volume and said sequential device groupafter said full backup in response to an update of said logical volume;and executing a partial backup by which partial data that are dataequivalent to a difference between said logical volume and saidsequential device group are specified by using said updated differentialmanagement information, information necessary for restoration that isnecessary to restore a data group located in said updated logical volumeby using said partial data is recorded in said sequential device group,and said partial data are backed up from said updated logical volume tosaid sequential device group a backup management storage sectionoperable to store backup unit management information representing, as abackup unit, a storage area of said sequential device group, that hasbeen consumed by a backup to said sequential device group, and a backupunit management section operable to add, to said backup unit managementinformation, information representing, as one backup unit, the storagearea that has been consumed by said backup when said full backup or saidpartial backup is completed, wherein said backup unit management sectioncomprises, for each backup unit, a backup unit identifier, a backupclass representing a class of backup, and a sequence informationrepresenting a sequence of backup in said backup unit managementinformation, and said partial backup section is operable to specify abackup unit having recorded therein backup of data necessary forrestoration of said partial backup based on the sequence information andbackup class in said backup unit management information and comprises abackup unit identifier of said specified backup unit and a backup classindicating that this is a partial backup in said information necessaryfor restoration.
 14. The backup method according to claim 13, wherein:said updated differential management information is included in saidinformation necessary for restoration, and said updated differentialmanagement information is reset in the case where said partial backup isconducted, and said reset differential management information is updatedin the case where said logical volume is thereafter updated.
 15. Thebackup method according to claim 13, wherein: said differentialmanagement information is a bit map, each bit of said bit mapcorresponds to each volume portion of said logical volume, and a storagesize of said volume portion corresponding to the bit of said bit map anda storage capacity of said logical volume are included in saidinformation necessary for restoration.
 16. The backup method accordingto claim 13, wherein: said updated logical volume is restored by usingsaid information necessary for restoration that is recorded in saidsequential device group.
 17. The backup method according to claim 13,wherein: said differential management information is a bit map, each bitof said bit map corresponds to each volume portion of said logicalvolume, said updated bit map, a storage size of said volume portioncorresponding to the bit of said bit map, and a storage capacity of saidlogical volume are included in said information necessary forrestoration, in said partial backup, said information necessary forrestoration and said partial data are recorded on the downstream sidefrom said all data that are recorded by said full backup, and at thistime said information necessary for restoration is recorded on theupstream side of said sequential device group from said partial data,said updated bit map is reset in the case where said partial backup isconducted and said reset bit map is updated in the case where saidlogical volume is thereafter updated, and said partial backup is any oneof a differential backup and an incremental backup.